Comparing mixed media and conventional slow sand filters for arsenic - PowerPoint PPT Presentation

Comparing mixed media and conventional slow sand filters for arsenic removal from groundwater K.M. Śmiech , A. Tolsma, T. Kovács , R. Bekius, V. Dalbosco, K. Yasadi, L.Groendijk , L.L.F. Agostinho​ Athens, September 2016 1

Outlook • Background: arsenic contamination of groundwater in Bangladesh • Methods • Setup design • Results  As removal efficiency  Vertical As concentration profiles  Raman analysis of F2 media • Conclusions 2

Arsenic contamination of groundwater in Bangladesh • Arsenic in drinking water via hand tube wells • Chakraborti et al. (2010): 36 million people  As > 10 µg L -1 (WHO guideline) • 22 million people  As > 5 0 µg L -1 (Bangladesh government) • • Health risks: • Skin lesions • Lung irritation • Cancer (skin, bladder...) • Solution: • SSF augmented with iron Chakraborti et al. (2010) Status of groundwater arsenic contamination in Bangladesh. A 14-year study report. Water Research 2010, 44 (19), 5789-5802 3

Methods • Three filters:  F1: Conventional (reference)  F2: Corrosive iron matter (CIM)  F3: Iron coated sand • Filtration rate: 6 L h -1 • Continuous operation for 260 days • Inlet As concentration: 70 μ g L -1 • Constant temp. 26 ° C • Online measurements:  pH  Redox potential  Electrical conductivity • Total As analysis in inlet and outlet twice per day • Total As samples along the filter column • Raman analysis of solid filter media 4

Setup design 5

As removal efficiency 6

Vertical As concentration profiles 7

Raman analysis of F2 media Raman spectroscopy: • 80% lepidocrocrite (ɣ -FeOOH) • 20% hydrous ferric oxides • traces geothite (α -FeOOH) • no magnetite Mass balance DO and Fe: • 80% CIM oxidized 2- occupying surface sites 3- , CO 3 F3: lower As removal efficiency due to PO 4 8

Conclusions • SSF augmented with CIM could efficiently remove As below the 10 µg L -1 WHO guideline for a prolonged time of continuous operation (200 days, 6 L d -1 ) • As removal occurred inside CIM layer • 80% CIM oxidized to lepidocrocite and HFO • Active sites in iron coated sand occupied by 3- and CO 3 2- during retreatment, preventing PO 4 efficient As removal 9

Acknowledgements 10

Thank you very much! Questions? karolina.smiech@hvhl.nl 11